Zachary made this at preschool and loved it, so we gave it a whirl at home, too. It was very fun for the kids, and yummy, too. It would be easy to whip up the pumpkin layer not in a bag, too, if you aren't after the bag experience.
First place graham crackers into a gallon sized ziploc. Since there were 6 of us I used 6 crackers. Zachary told us to crush it with a "roller coaster" and although I think a rolling pin would have worked, we went with the hammer method. In Zachary's class they put them in the bottom of dixie cups. We put them in the bottom of 6 bowls.
In another gallon bag pour 1 1/3 cup cold milk and 2 4oz boxes of instant vanilla pudding. Remove the air, close the bag and squish, squish, squish.
Add 1 15oz can of pumpkin, 1 tsp cinnamon and 1/2 tsp ginger. Remove air, seal bag, and squish, squish, squish.
Cut a hole in the corner of the bag and squeeze onto the top of the graham crackers. We had enough for 6 healthy servings in the bowls, plus another full bowl left over.
We put them into the fridge to eat after dinner, but they would be ready to eat right away as well. Top with a dollop of whipped cream, if desired.